text:
Between land and sea, which route is preferred?
Suppose that you have to connect two destinations like Phoenix and Anchorage, which are 5850km apart. Now, you have two choices: to either fly over the land, or completely fly over Bering Sea (Arctic Ocean). So, what would be the better route to choose? Currently, the route is partially over the sea and partially over the land.
Also, this is just a case, in general out of land and sea, which route is preferred? One common argument is that you are safer by flying over land in case of an emergency, but are there any aerodynamic concerns also involved?

A flight from Phoenix to Anchorage will not fly over Bering Sea, as it is a lot more on the West. The example flight I found stays over ground most of the time. I think the actual answer to your question will be that considering the factors applied (weather, political situation etc.), the flight will always choose the shortest, most economical route.

The ususally preferred path will be the shortest, as any additional km flown will require extra fuel.
For the example you propose we can look at what companies actually do (US653 of 5 July 2015):

As you can observe they fly pretty close to the great circle passing through the two airports, meaning that they will fly partially over the ocean.
This poses no additional risks, as the shoreline is never really far away and in case of emergency an alternate airport will most likely always be within reach.

At the cruising altitude of most airliners, there is no noticeable aerodynamic difference between being over land or over sea. At lower levels, being over sea would typically offer less turbulence, in part because as the ground warms you can encounter rising air thermals.
Generally, airliners fly whatever route provides the shortest time, which is not always the shortest distance, often called the Great Circle route. The GC route is not always quickest because of jetstream winds.
One thing to consider when choosing between an over-land or over-sea route is the distance to another airport should an engine fail. You might have heard of ETOPS. Basically, twin engined aircraft must fly within a certain distance of a suitable landing site - often 2 or 3 hours of flying time on one engine. In the middle of the ocean the quickest route may take the aircraft outside of this range, so it will have to fly closer to land, or even in certain remote parts of the world, still over land.
Another consideration is life rafts. They are legally required when flying more than 25 miles (if I recall correctly) out to sea. Life rafts add weight and therefore cost so some airlines have actually removed life rafts from their aircraft, or at least only have a few of their jets allocated for flights over water.

Life rafts or life vests? The later, sure, but you can't remove life rafts from most aircraft since the evacuation slides double as life rafts in most of them.

@JanHudec I suppose so, but according to that article the 737s are capable of having them removed.


text:
What would happen if the blades of a variable pitch prop did not all have the same pitch?
What would happen if one or more of the blades (but not all) on a variable pitch prop would not tilt at the same angle as the other ones?
Could this situation happen or is the technology so advanced or stable that it would be basically impossible?
Should it happen, besides vibration (most probably due to imbalance factors,) what other effect could there be? How would pilots solve this emergency (if it can be called so?)

It is a single mechanism, what you are proposing will mean that the mechanism is actually broken

Could it happen that if the mechanism breaks part of it would still continue functioning? Something like in some car gearboxes where you might get some gears, but not others.

I ca not help you here... I don not know.

it is not always a single mechanism.  many designs involve each prop blade having its own control linkage.

Never say never, but that's not a prop malfunction that I've heard of or that was ever addressed in the turboprops that I've flown.  We had various prop malfunctions, but the ways that things could fail that we considered would pretty much leave all blades in the same place.  So without claiming that it could not, ever, ever, no way no how, not in all possibility ever happen, I'll say that it's not very likely.
If you did get something like that, the vibration would probably be bad enough that you'd shut the engine down, and at that point the interesting question would be, do all the blades feather for you?  (The answer to that probably depends on what type of prop you have and what specific failure mode led to the condition in the first place, and now we're into too much speculation for any answer to be very enlightening.)

Good answer. Just to comment, I do not fly. My question came out after a flight on a ATR72 a couple of days ago.

Yes the prop blades can be mis-indexed on older model turboprop systems. the Hamilton Sundstrand 54H60 system uses a hydro-mechanical prop control and a dome to change pitch. When reinstalling the dome, it is possible to mis-index the blades so that they do not all have the same blade angle. There are however ways to check for this prior to starting the engine so I'm not aware of any engine being started with mis-indexed blades. The newer systems like the Hamilton Sundstrand NP2000 and Dowty R391 have a pitch change actuator that locks in the trunion bearings on the blade butts. This system prevents mis-indexing of the blades.

I have a friend who owned a homebuilt aircraft with a ground adjustable prop.  They had a terrible vibration problem that they could not diagnose.  They spent months or years trying to get the bottom of it.
Through that process, they switched from an experimental automotive engine to a traditional aircraft engine.  They had their prop re-balanced multiple times.  All of these things made no improvement.
Eventually, they figured out that one of the blades was off by 1 degree from the others.  Re-adjusting the prop and everything was glass smooth.
This took several years and many dollars to sort out.  During this period, they were not comfortable flying the aircraft -- so there was also the lost time value in airplane ownership.

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text:
Will talking about sleep problems with my doctor jeopardize my medical?
I am asking this for someone I know who's up in years but still under 60, and is a fellow pilot.  He brought this question up:
"I am concerned that I might have some moderate sleep problems - doubtful it's narcolepsy, and I've driven (and flown) safely for years and the worst is feeling tired.  My thought is to check on blood levels and maybe EKG stuff etc..  Perhaps there is something that's actually detectable.  Perhaps there is medication that reduces the tiredness.  If I go to a doctor and bring these up, will it jeopardize my medical?"
Your thoughts?  Appreciate your feedback - my friend is not an internet person at all :)

Your friend should be worrying about his health rather than his license. And the country matters a lot here but no one should make their medical decisions on random advice from the internet. Having said all that, a reasonable thing to do is to find an Aviation Medical Examiner (or local equivalent) and ask them for a consultation; if your friend is in the US, he could also join AOPA and ask them. There are also many threads on AOPA's forums (members only) about sleep apnea, required medical reporting etc.

First of all what country are you referring to?

In the US the HIPAA rules often provide you with confidentiality but there are several circumstances that allow your doctor to provide info without your consent and being a pilot qualifies. It allows them to, but only requires them to in situations where a crime might be involved, i.e. physical abuse.
The concern would probably not be that your doctor will tell the FAA (although they probably could if they were truly concerned), it would be that you would be required to tell your FAA examiner of any diagnosis. I believe it's a felony not to.
If it's sleep apnea he's concerned about (you said sleep problem, non-narcolepsy - I'm not a doctor so I'm just offering what i know about a very common sleep problem) then there are ways to get a special issuance medical certificate.
I'm not a pilot but a driver and I have to have a DOT medical card. The way sleep apnea is usually treated is by CPAP. For the DOT physical, If you are on CPAP you have to bring the machine to your physical so the examiner can check the data and verify that you have been using it (I think 75% of the time but don't quote me on that). I checked and the FAA has similar rules.

I agree with Pondlife that one's health should trump licensing concerns, and nobody should be flying if they are at risk of dozing off. But I definitely understand your friend's situation. I suspected I had apnea but I refused to go to a sleep study because I did not want the diagnosis. What if I couldn't deal with CPAP? My dad was on CPAP for 30 years but he rarely used it because it was too uncomfortable. Then I'd be forced to use it to keep my job.
Fortunately my situation resolved itself (I don't have apnea) but I understand why he's reticent to mention it to his doctor.

Sleep problems are a concern to the FAA. Lack of sleep or not having restful sleep contributes to fatigue, and fatigue is one of the 12, aka 'The Dirty Dozen,' leading factors for accidents, incidents and mishaps. This is a serious matter for all parties involved.
Here are a couple good resources:
http://www.aopa.org/Pilot-Resources/Medical/Medical-Certification-and-Conditions/Sleep-Disorders
http://www.skybrary.aero/index.php/The_Human_Factors_%22Dirty_Dozen%22
Lack of good quality sleep not only contributes to fatigue, but it is stressful on the body and mind. It magnifies the existing stress. Tell your friend to take care of themselves first, and then they could consider working with a local AME that specializes in complex medical cases.

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text:
Does a 1lb crow expend only 7.68 Watts to fly at 37 km/h?
The Wright brothers and the 1 pound crow that flies at 37 km/h expending just 7.68 W
In an 1905 letter to Octave Chanute, Wilbur Wright evaluated the power, used by a 1 lb bird to fly at 34 ft/s, utilizing a relation that can be rewritten as:
eff x Power = Thrust X Speed = Drag x Speed,
where: eff (the efficiency of the crow) = 75%, Drag/Lift = Drag/(mg) = 1/8 and mg = 1 lbf.
In consequence, Power = (1 lbf x (1/8) x 34 ft/s ) / 75% = 7.68 W.

"The power consumed by any bird or flying machine may be figured from the formula wv/ac, in which w = weight, v = velocity, 1/a = ratio of drift to lift, and 1/c = efficiency of the screws or wings as propellers. In the case of the crow flying at 34 ft. per second, or 2,100 ft. per minute, I would fix the value of l/a at 1/8, and 1/c at 1/.75; when we have (1 x 2100)/(8 x .75) = 350 ft. lbs. per pound of weight.1 The minimum value of l/a may be rendered independent of velocity by regulating the size of the wings. The value of 1/c is about the practical limit of the efficiency of screws under usual conditions, and I see no reason for believing that wings are more efficient than screws, as propellers. It is quite incredible that, when flapping, the wing can be kept at the optimum angle at every point, as in soaring; and there are losses due to the fact that the pressure is not vertical throughout the stroke. Although I think 25 percent a fair estimate of the probable loss from both sources.
  Birds unquestionably develop power many times greater than is consumed by our Flyer, per pound weight. if you will fix in your mind the distance within which a small bird acquires full speed, say 30 miles an hour, and then figure the power necessary to accelerate its weight to this velocity, I think you will be astonished. I know I was almost dumbfounded, especially in view of the fact that the power available for acceleration is over and above that used in flying. I shall be curious to know what distance you fix upon as that within which a sparrow acquires full speed.",
Letter of Wilbur Wright to Octave Chanute, Dayton, March 11, 1905

7.68 W/lb seems a quite low figure as long as, it's generally accepted that any model plane with less than 50W/lb is going to struggle (see The Watts Per Pound rule)
Does a crow only expend 7.68 W/lb or at least it is possible to build a model plane able to fly at 37.3 km/h (34 ft/s) developing just 7.68 W/lb shaft power?

A crow doesn't have a shaft to power. A prop is not very efficient either.

ratchet freak, read carefully the text I quoted because W. Wright gives there some explanations that will clarify your remarks.

Simple answer: we suck compared to nature. Although in our defence, nature has had more practice.

Nature never invented a wheel though.

I came here expecting an eventual comparison of the crow to a European swallow carrying a coconut. Learned some historic trivia instead.

The number cited by Orville looks quite reasonable. The crow is just cruising along, not banking, accelerating or climbing.
Now add a climb speed of just 1 meter (3.3 feet) per second, and the additional power is 5,93 W. Let it circle with 60° bank angle, which would double the required lift, and the power for staying aloft increases to 15.36 W.
Next comes the flight speed, which goes up with the root of the wing loading. The American crow has a wing chord between 25 and 33 cm and a wing span between 85 and 100 cm. Taking the average puts their wing area at maybe 0.25 m² (it is almost rectangular, after all), and their wing loading at 1.8 kg/m². I would expect that a battery-powered model would have a higher wing loading, maybe 5 kg/m². The required power goes up with the third power of speed, and the speed itself increases with the square root of the wing loading. This makes the model of the crow fly at 62 km/h and consume a power of 35.5 W - just for straight and level flight. Add some margin for acceleration, banking flight and climbing, and the 50W/lb rule looks quite reasonable.

I need an example of ~ 1 lb model plane that can fly at about 10 m/s (36 km/h) using maximum 10 W. It is quite clear that 7.68 W/lb x 745 lb x 75%/66% = 8.77 hp which is quite close to the 8.73 hp the two brothers estimated they needed to fly their 745 lb, 66% efficient, 1903 plane. In other words the Wright brothers simply assumed the efficiency of the bird is 75% and scaled down to 1 lb the power needed for their 745 lb plane to fly. This is pure math.

An airplane which needs 10 W for straight and level flight will have maybe three times as much power installed to be useable. Don't expect to find one which has a 10 W engine installed, even though it will need only 10 W for flying at its best efficiency. On the other hand, the Flyer I could only fly straight - it needed already all the installed power for flying at its best efficiency

Any model plane that stays in the air can be useful for something. If W. Wright was right, there should be 1 lb planes that fly using just 7.68 W.

I made a solar model airplane (the LUSA, facebook.com/LUSAonline) that at ~2 pounds required 18 watts to fly. And it wasnt even uber-optimized from an aerodynamic point of view....

@Caterpillaraoz: What wing loading does it have? I bet it is quite a bit below the 5 kg/m² that I used for the example.


text:
What are the factors considered while placing a propeller on a plane?
I have read the post where it describes about the push and pull configurations of the engine, advantages/dis-advantages in them but not the purpose.
I have seen images of a figter where the propellers are placed both at the front as well as back, such as the Dornier Do 335.
(Image Source: WikiPedia - Author: Ad Meskens)
Later there are some downsized planes which are remotely controlled vehicles like the MQ-9 Reaper where the propellers are placed at the rear, Miniature UAV have the props in the front (sometimes even the direction of the propeller also vary)
Is it the size which makes the difference or the purpose?
Also what was the scenario due to which the designers had to go in for a varying propellers why not stick to the simple front facing propellers (which are placed either on the wings or in the front why to go for propellers with backward design/rear placed)?

@user285 Was your edit and removal of the example image I provided intended or just a mistake as your edit overlapped mine?

@SentryRaven I had edited at the same time as yours so it overlapped

The biggest factor is familiarity: What has worked before?
Other factors are:

Propeller size: Slow-turning propellers driven by powerful engines have a big diameter. This is desirable because it improves efficiency. However, now the propeller cannot be placed behind the wheels if the rotation angle should not be restricted.
Engine location: Driveshafts cost weight and run the risk of resonance problems, so the propeller should be directly in front or at the back of the engine. The engine location is dictated by the desired mass distribution, cooling, the pilot's field of vision, and space demands.
Interference: This includes all factors like prop wash and swirl. Putting the propeller ahead of control surfaces or flaps improves their effectiveness at low speed. Conversely, the increased flow speed increases friction drag on the surfaces wetted by the propeller's slipstream.
Stability: The propeller acts like an additional small wing and creates lift and side force when not exactly perpendicular to the inflowing air.
Engine-out performance: Multi-engined aircraft should still be flyable with one dead engine. This is an interaction between propeller location and control surfaces, and to minimize drag, those control surfaces should be as small as possible. Thus, the propeller should be close to the center of gravity.

The rear propeller is more efficient, because it helps to prevent separation on the surfaces ahead of it, and its slipstream will not increase the friction drag. However, integrating a propeller at the back of an aircraft is hard, so few designs (apart from those in this answer) made use of it. Notable examples are:

A range of British fighters during the early years of WW I, when only the Germans had mastered the technology of synchronized machine guns.
The Zeppelin airships. Their gondolas had rear-mounted propellers.
The Convair B-36. The pusher location in the wing was selected for better efficiency, but created cooling problems for the engines.
The Learfan, started during the first oil shock and designed for efficiency. Two PT-6 drove a single pusher propeller.
The Piaggio P-180 Avanti, which was designed a few years later and much for the same reason as the Learfan.

Also, Claude Dornier had used two engines in one engine pod, driving a propeller each at the front and at the back, as early as 1915, when he worked for Zeppelin on a giant metal flying boat. This became a common theme on many Dornier aircraft, especially the flying boats, and on the Zeppelin Staaken giant bombers. The last example of this range is the Dornier Seastar, designed in the late 1970s.

It is the purpose. Each configuration has it's own advantages and disadvantages. This is already explained in Why are push-propellers so rare, yet they are still around? and this answer in particular.
In case of Do335, the reason is that they wanted two engines, but keep the engines on the centreline. This results in lower drag due to lower frontal area and better manoeuvrability due to lower moment of inertia as the engines are closer to centre of gravity. The pusher propeller itself reduces the manoeuvrability somewhat though.
In case of MQ-9 it simply matter of providing space and clear view for the radar and cameras in front while the reduced manoeuvrability does not matter much in this case.


text:
What coming changes might render current IFR equipment worthless in the foreseeable future?
I'm shopping for my first aircraft.  I have found a very well cared for 172 that is VFR.  I also found an IFR-certified 172 that is higher time and cosmetically is showing its age.  I inquired about the expense of updating the VFR plane to IFR and the seller mentioned that due to some upcoming changes in IFR requirements even a plane that is IFR rated today may require a substantial investment to keep it IFR.
I've done a lot of searching and can't find anything to substantiate that statement.  The closest thing I found was an article from the AOPA way back in 1997 where the FAA had proposed rule changes that would have made a lot of (then) IFR compliant GPS units non-compliant.
What, if any, regulatory changes are on the horizon that might render the IFR certified equipment I buy today worthless tomorrow in the context of IFR?

He may be referring to the "ADS-B Out" requirement, which is becoming mandatory in 2020 (unless delayed).  However, that is not an IFR requirement, its an "every-plane" requirement.

I've added a faa-regulations tag because I assume you only fly in FAA airspace. Please adjust if necessary.

Also of interest: FAA NextGen.

At the moment the answer is "None" - with two exceptions:

LORAN receivers
These are already worthless because the US has shut down our LORAN chains.
They are jokingly referred to as "IFR-Certified Lead Bricks".
ADFs
The FAA is killing off NDBs one by one - an ADF is basically an expensive, drag-producing AM Radio in many parts of the country, and its utility is in steady decline.

Other than that the core IFR technologies are pretty much sticking around:

VOR/LOC/ILS isn't going anywhere.
Some VORs are getting decommissioned, but even the bleakest plans call for the FAA to maintain a "minimal operational network" of VORs as a backup in the event of trouble with the GPS satellites..
DME is sticking around.
Lots of planes flying around use DME still, and there are lots of DME approaches which serve as good backups for GPS approaches.
(WAAS) GPS is the current "best technology" & isn't going away soon.
The FAA LOVES WAAS GPS. It lets them get ILS-type approaches to pretty much any runway without expensive ground equipment to install/maintain/test. If you have an IFR-Certified WAAS GPS in your aircraft you're on the cutting edge of IFR navigation equipment, even if the GPS itself is older-generation technology (such as the popular Garmin 430W).
If your GPS is not WAAS capable it's still going to be usable, but it's much more limited. It may also pose some problems for you down the road (see below).

Some equipment regulations are changing (as part of the ADS-B Out mandate coming in 2020), but that's not an IFR-specific thing.
The crux of the ADS-B Out mandate is if you want to fly in airspace where a Mode C transponder is currently required you will need two things in your aircraft (if they're not already installed):

An ADS-B Out transmitter to broadcast your position.
This can be achieved in two ways:
A Mode S transponder with Extended Squitter (1090ES); or
A 987MHz Universal Access Transceiver (UAT)
A suitably accurate position source to talk to the transmitter.
Currently that means a WAAS GPS - either a panel-mounted device or a separate "blind" box.

The cost of complying with this mandate falls somewhere within a wide range: If you want a modern WAAS GPS with a touchscreen interface that will let you fly GPS approaches and a new transponder to do the broadcasting part you're going to spend a lot more money than if you install a Universal Access Transceiver and blind GPS source that do the absolute minimum required to comply.


text:
What details do EICAS systems provide?
I was reading this article about EICAS:

Engine-indicating and crew-alerting system (EICAS) includes
  instrumentation of various engine parameters, including for example
  revolutions per minute, temperature values, fuel flow and quantity,
  oil pressure etc. Typical other aircraft systems monitored by EICAS
  are for example hydraulic, pneumatic, electrical, deicing,
  environmental and control surface systems. EICAS has high connectivity
  & provides data acquisition and routing.(source: Wikipedia)

Wikipedia article doesn't explain EICAS functionality very well, specially on the matter of the Crew-alerting System.
I'm interested to know more about this system... So here is my questions:

I'm correct to assume that EICAS is a vital instrument for glass cockpits?
Is every fault displayed there? (ie. Radio failure, air packs malfunctioning, etc...)
What is the difference between red messages and yellow messages?
How much detail can a pilot get from its messages?

The EICAS will have the engine instruments and the crew alerting system in one display.  It is a vital instrument because it displays engine parameters, fuel, the crew alert system and other systems information depending on the specific airplane.
The CAS (crew alerting) functionality of the EICAS replaces the illuminated fault buttons in older airplanes.

YSSYguy CC-BY-SA 3.0
The electronic CAS that is part of an EICAS display is a superset of these old panels and can display a much bigger set of alerts.  The specific alerts that can be shown will cover most error and failure modes the airplane systems can reasonably encounter.  Cautions are yellow in color and will illuminate the master caution and sound an audible chime.  Warnings are red in color and will
illuminate the master warning and sound the triple chime (and the fire bell for certain conditions).  There may also be advisory messages displayed in another color, e.g. cyan, on the EICAS.

 EMB-145 EICAS.  The CAS is the upper right portion of the display
The messages themselves are terse and not detailed, though detail can be inferred from the pre-defined message text.  Warnings and cautions that are displayed can be addressed with memory immediate action items (memorized checklists) and/or the QRH (quick reference handbook) which defines the procedures for dealing with problems in a verbose checklist flowchart.  The QRH will be indexed by the messages on the CAS so they can be easily found and referenced.

Is there any difference between EICAS and ECAM?

ECAM - Electronic Centralized Aircraft Monitor - is the Airbus system that provides Engine/Warning Display (E/WD) and System Display (SD). Different names, slightly different system architecture, same basic function.

As far as I know EICAS is used in Boeing aircraft. The wiki page you provided has a link to Airbus system as well which is much more complex and detailed. Not every fault is displayed there. Detailed list is available in Boeing manuals. For example 737NG: http://www.smartcockpit.com/plane/boeing/b737ng.html Look under Engines. Interestingly nowhere in manuals it's referenced by EICAS. Maybe because it's really basic for 737NG. Usually red is critical and yellow or amber is caution. And yes it's important and critical engine parameters are shown there.

Airbus calls their system https://en.wikipedia.org/wiki/Electronic_centralised_aircraft_monitor. While they aren't exactly the same, my understanding is that they are fairly similar when it comes to comparing the most recent models of aircraft.


text:
Must RAIM be checked in flight before every GPS approach or is a preflight check acceptable?
My instructor has been teaching me to run a RAIM check for each RNAV approach we do.  For some flights this can be 4 or more RAIM checks for the various airports/approaches and adds significantly to the workload.
I started doing some research and I think I've gathered a few things. First RAIM applies over large areas, not singular GPS points (makes sense), the FAA provides a tool to determine RAIM availability from the ground as part of preflight, and last that a RAIM check while briefing the approach seems Like it might not be necessary since the GPS is required to run a RAIM check 2 miles prior to the FAF.  Additionally since the GPS has no way to know about unexpected NOTAM announced outages the 430 RAIM precalculation is a bit less reliable.
Is it a requirement to run the manual RAIM check in flight or is it more appropriate to use the FAA tools and determine it as part of preflight preparation?

It can be confusing to read the AIM and FAA publications if you aren’t aware of the difference between the formal definition of GPS and the colloquial definition. Equipment certified under TSO−C145() or TSO−C146() are referred to as augmented GPS, WAAS-capable GPS, or WAAS. Prior to WAAS availability, GPS systems were certified under TSO-C129() or TSO-C196(). The pre-WAAS systems were certified as supplementary navigation and require a RAIM check. WAAS systems do not require a RAIM check.

You should check the FAA site in your pre-flight. If you check the FAA site for the RAIM status at your destination, you will know if you can plan on an RNAV approach. You won’t be able to fly an RNAV approach unless the unit passes the RAIM test when you are there.

From what I remember (I may be wrong), the 430 indicates on the screen during an approach if the RAIM check was successful. I don't remember ever having to check it manually, my instructor just had me confirm the indication was there before continuing past the FAF. If the RAIM indicator wasn't there, we went missed.

The FAA website predicts pre-flight whether RAIM will be available
The RAIM algorithm will tell you during your flight if GPS is working correctly.
The pre-flight FAA website check is not a substitute for the use of the RAIM function during flight. It will only show whether the RAIM function is available during flight.

RAIM stands for Receiver Autonomous Integrity Monitor. It is a part of aviation graded GPS receivers that checks consistency of all used GPS satellite signals in order to raise an alert if the GPS system is not working correctly.
For RAIM to work, there must be at least 5 usable satellites in view of the GPS receiver. For GPS without RAIM, at least 4 satellites are needed. If there are only 4 satellites visible, or more than 5 but with an unfavourable geometry, RAIM cannot work and therefore the GPS receiver cannot be certain that the produce position fix is correct.
The FAA website predicts the availability of RAIM; based on the constellation of GPS and the health status of its satellites, the route and the time of flight it is possible to calculate  whether RAIM is available for your flight. This can be done before you take-off.
If there is no RAIM available during part of your flight, you can't rely on GPS during that part. The GPS may still work fine, but there is no way to check its integrity. A single fault in a GPS satellite or, more likely, a corruption in the downlinked GPS satellite almanac will cause the position fix to be off. You must use alternative navigation means if GPS RAIM is not available.
The FAA website does not say anything about the actual quality of the GPS system during your flight. This is what RAIM does. It continuously monitors all satellite signals for consistency and flags any inconsistencies.  There are various categories of RAIM such as Fault Detection and Fault Detection & Exclusion but all RAIM algorithms will give you a containment radius.
The containment radius is the maximum size that a position error can grow due to a fault in the GPS system without the RAIM algorithm being able to detect it. The value of the containment radius depends on the geometry of the satellites.
The requirements for the value of the containment radius depend on the flight phase. For En-Route mode the RAIM containment radius value should be under 2 NM, terminal mode under 1 NM, and approach mode 0.3 NM.

This reminded me to update the GPS data on my phone. With luck I'll get more accurate readings on my run tracking! :)

@DeltaLima Good description of RAIM, but the issue here is the operation of the installed system (tag indicates GNS430 which is an older non-WAAS design).  IIRC, installation of those units required a RAIM annunciator which would provide RAIM failure alerts with no pilot action.  The answer should be in the Aircraft Flight Manual Supplement (AFMS) for the installed GPS.  An AFMS is required as part of the STC approving the installation of the GPS.

@Gerry - The original asker may not have wanted to create a tag for gns430w since the two devices are so similar.

@SteveV.  Similar, yes; but they provide different capabilities and the answer will depend on the actual unit installed. Also, just because the unit has a capability doesn't mean it was installed in a manner that can use it. How you use an installed piece of equipment (an appliance in FAA certification terms) is controlled by the AFMS which becomes part of the aircraft's flight manual under the STC. The best answer should be to 'read the manual'.

This answer could be improved by referencing the applicable requirements for IFR certified GPS installations conforming to the various TSOs. For example WAAS installations do not need a pre-flight RAIM check, wheras non-WAAS receivers generally need a pre-flight RAIM check. See AC 90-108.

Answer lies on AIM 5-1-16 "rnav and RNP operations" paragraph f:

f. During the pre−flight planning phase RAIM prediction must be
  performed if TSO−C129() equipment is used to solely satisfy the RNAV
  and RNP requirement [...] Operators may satisfy the predictive RAIM
  requirement through any one of the following methods: [...] 2.
  Operators may use the FAA en route and terminal RAIM prediction
  website: www.raimprediction.net; 3. Operators may contact a Flight
  Service Station (not DUATS) 3. Operators may use a third party
  interface, incorporating FAA/VOLPE RAIM prediction data [...]

Conclusion: once you check the route of flight through SAPT on FAA en route and terminal ram prediction website, it is good for all those RNAV IAP approaches!
While flying from Phoenix, Westwind school. Similar question came to me.. Where all of instrument student and most instructor does check Raim availability immediately after Engine starts and turn on the MFD on G1000 C172S nav III.
This will do raim prediction (under TSO C129 equipment's internal capacity) for that location (because it's default search location is p.pos- present position) and +/- 15 minutes.  But if you have not inserted RNAV Approach in flight and have not activated the approach, it is not going to calculate the ETA/ETE to the target airport. Similarly, if you have just loaded the RNAV Approach on flight plan and not have activated, then it is not going to select the destination airport (or missed approach waypoint) for RAIM prediction. Contrary to you having to check up to 4 RNAV approach destination airport, we've been checking only the ramp of departure airport...
Remarks: All the IFR-certified GPS unit will do RAIM check 2 NM prior to reaching FAF. So during flight we do not need to. As long as we have performed prediction throughout the route. We will know whether to avoid that airport's RNAV approach, just in case prediction says 5+min of RAIM service might not be available for some part of leg.


text:
Why wasn't Saint-Exupéry able to cover more distance before his 1935 desert crash?
Is there any source that provides more details on Saint-Exupéry's desert crash in 1935 than Wikipedia does:

On 30 December 1935, at 2:45 a.m., after 19 hours and 44 minutes in the air, Saint-Exupéry, along with his mechanic-navigator André Prévot, crashed in the Libyan desert, during an attempt to break the speed record in a Paris-to-Saigon air race and win a prize of 150,000 francs. The crash site is thought to have been near the Wadi Natrun valley, close to the Nile Delta.

I find hard to understand how flying for nearly 20 hours between Paris and Saigon can lead any plane to as short distance as middle Libya?
Google Maps shows a distance of approx. 1950 miles straight line between Paris and Wadi Natrun, which gives us nearly exactly 100 mph of speed, which is only half of Caudron Simoun's speed.
What am I missing? Is it / was it a regular practice to fly "that slow" on such large distances?
There are 6000 more miles to fly between Wadi Natrun and Saigon, according again to Google Maps. With 100 mph we have 60 hours of flight plus additional 20 hours already flown. Which gives us a total distance of 8000 miles or 80 hours with this speed. Was there any aircraft and pilot, in 1935, able to manage such trip, even assuming breaks in flight for fuel refilling and resting?

Wikipedia shows the 1935 speed record as much higher: 13 September 1935, Howard Hughes, 354.4 mph, 567.12 kmh, Hughes H-1 Racer landplane. I don't know what range it had tho.

And more:  Hughes later implemented minor changes to the H-1 Racer to make it more suitable for a transcontinental speed record attempt. The most significant change was the fitting of a new, longer set of wings that gave the aircraft a lower wing loading. On January 19, 1937, a year and a half after his previous landplane speed record in the H-1, Hughes set a new transcontinental speed record by flying non-stop from Los Angeles to New York City in 7 hours, 28 minutes and 25 seconds.

From the Smithsonian Air and Space Museum: His average speed over the 2,490-mile course was 332 mph, and this nonstop flight was truly an outstanding accomplishment.

@CrossRoads I have a trouble understanding what are you talking about, maybe due to lack of link / cite. How can his course be 2490 files, if they crashed after 1950 mile flight? How can his average speed be 332 mph, if they flown 2000 miles in 20 hours so their average speed, as per my calculation, is around 100 mph. Are we talking about the same flight?

The 332 mph/2490 miles refers to Howard Hughes' flights, in reference to the last question of the original post about any aircraft being able to make the flight.

This site has more details on why it took so long to get to Libya
https://www.thisdayinaviation.com/30-december-1935-wind-sand-stars/

After taking off at Paris, Saint Exupéry followed the Seine to the valley of the Loire and continued south, crossing the southern coast of France near Marseilles. The fliers had been over the Mediterranean Sea for a short while when they saw fuel leaking from the left wing. Prévot calculated that they had lost 20 gallons (76 liters) of fuel. They turned back and landed at Marignane to repair the leak and refuel before continuing.  Saint Exupéry wrote, “I drank a cup of coffee while the time lost hurt like an open wound.”
Once again heading across the Mediterranean toward Tunis, they encountered low clouds and heavy rain which forced them down to just 60 feet (18 meters) over the water. They flew along the coast of Sardinia as the weather improved.
F-ANRY crossed the coast of Africa at Bizerte, Tunisia, and about fifteen minutes later landed to refuel. With two hours of daylight remaining, Saint Exupéry and Prévot took off again, now heading toward Benghazi, Libya. They landed there at 11:00 p.m., local time, and in just twenty minutes the airplane had been refueled and once more, they were airborne.
Flying east after moonset, Saint Exupéry and Prévot were in total darkness. After three hours a faint glow of his navigation lights on the airplane’s wingtips told Saint Exupéry that he had flown into clouds, with visibility measured in just feet.
At a time when there were no navigation aids, pilots had to navigate by their compass, airspeed indicator and clock. Though Saint Exupéry had met with meteorologists to plan his flight, there was no way to update the weather information after takeoff. He had no way of knowing whether an expected tailwind had held, or if it had changed; was his speed across the ground faster or slower than planned? Had the wind blown him right or left of course? Had the atmospheric pressure changed, causing his altimeter to read higher or lower than the airplane actually was? Flying across the emptiness of the  Sahara Desert with no landmarks, in total darkness and now just a few feet of visibility, he and Prévot could only guess at their position.
4 hours, 15 minutes after taking off from Benghazi, the C.630 crashed into gently rising terrain at 170 miles per hour (274 kilometers per hour).

More on the plane:

The Société des Avions Caudron C.630 Simoun was a four-place, single-engine, low-wing monoplane with fixed landing gear. It was built of wood, with the surface of the wings and fuselage covered in plywood sheet then covered with doped fabric. Carefully curved aluminum sheet metal covered the top and bottom of the fuselage. The C.630 was 8,70 meters (28 feet, 6½ inches) long with a wingspan of 10,40 meters (34 feet, 1½ inches) and height of 2,25 meters (7 feet, 4½ inches). The airplane’s gross weight was 1,230 kilograms (2,712 pounds).
The engine was an air-cooled, normally-aspirated 9.500 liter (579.736 cubic-inch-displacement) Renault Bengali 6Pri inverted inline six-cylinder overhead-valve (OHV) engine rated at 180 cheval vapeur (177.5 horsepower). The left-hand-tractor, direct-drive engine turned a two-bladed, metal Ratier variable-pitch propeller. The propeller could be set to coarse pitch by a mechanic prior to takeoff, then an air bladder mechanism could change it to fine pitch for cruise flight.
The C.630 had a maximum speed of 310 kilometers per hour (193 miles per hour). The service ceiling was 7,500 meters (24,606 feet) and normal range was 1,260 kilometers (783 miles). Twenty C.630s were built before production changed to the slightly improved C.631.

Not a lot different than my Cessna Cardinal, which is a little wider (35'6"), 4 seats, fixed gear, and 180 HP Lycoming engine with constant speed (variable pitch) prop totally controlled from within the cockpit. Service ceiling only 14,600 feet (altitude where climb rate drops to under 100 ft/min). Gross weight 2,500 lbs. Max speed (never exceed speed) is 192 mph, with max cruising speed of 158mph (speed not to exceed except in smooth air). Cardinal carries less fuel most likely, just 50 gallons, my best range at 10,000 ft is 615 miles.  I think our longest flight has been about 4 hours, can only listen to ATC for so long!

There is no information (neither in your answer nor in the cited text) on how much it took them for repairs of leaking fuel tank and refuelling, but I assume that this could take a couple of hours and cause the medium trip speed to be that low. Thank you for providing all these details.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How easy is it to make a connection to the aircraft pitot-static system?
I've recently discovered the device named Levil 2 AW which gives complete navigation functionalities, including Air Data computations once it is connected to the pitot-static system.
In this regard, generally speaking, is it really so easy to connect to the aircraft pitot-static system as it appears from both product description and related videos?

Depends, is this a TSO installation or non-TSO? I don't think the iLevil is TSO'd so you can probably only install this on homebuilt/experimentals, which means it should be a relatively simple process.

It's very easy to connect a component to the pitot and static systems: It's literally just basic plumbing (install a T fitting and connect the lines). For IFR certified aircraft a static system test will also be required (and a pitot pressure leakdown test would be advisable if the pitot system is opened).
The regulatory issues surrounding the installation are more complex regarding what kinds of devices may be installed on a certificated airframe and under what conditions they such devices could be used as a primary or standby reference for flying the aircraft, as Ron alluded to.


text:
How do airlines handle SIGMETS?
In general, what is the action taken by airlines when presented with a SIGMET in the projected route. Will they go around it, cancel the flight prior to takeoff, or simply fly thought it anyway?
As an example, there is a large SIGMET over the Sierra Nevada mountains right now due to high winds causing wind shear and moderate to severe turbulence. Knowing that severe turbulence can be a serious issue, would airlines, in general, cancel the flight, go around the area or simply fly anyway?
WSUS06 KKCI 250040
WS6N
SFON WS 250040
SIGMET NOVEMBER 2 VALID UNTIL 250440
CA NV
FROM 80N FMG TO 30ESE OAL TO 60NE EHF TO 50ESE RBL TO 80N FMG
OCNL SEV TURB BTN FL280 AND FL410. DUE TO WNDSHR ASSOCD WITH JTST
AND MTN WV ACT. RPTD BY ACFT. REPLACES NOVEMBER 1. CONDS CONTG
BYD 0440Z.

Source: aviationweather.gov

Your options, as you pointed out, are either to climb over this area, To go around it, to go under it, or wait until the segment expires or is expected to subside.
Another option available would be taken by this information with PIREPS.  What are pilots reporting happened to them in this air space at this time?   The SIGMET noted that there was occasional severe turbulence expected in that area which is pretty vague.  If there are a very large number of PIREPS widespread throughout that block of airspace, it’s a good bet that it is very turbulent throughout and may not be a good idea to penetrate it.  If the PIREPS are few and don’t repeat much turbulence in that airspace, then it may be advisable to fly through.  Just keep the speed at that recommend by the manufacturer for penetrating turbulence and keep the fasten seat belt signs on.

The chart you linked is not a SIGMET, it is a prognostic chart.
To answer your question, it depends on the nature and location of the weather. In the case of the example, nothing shown would stop a flight because the weather top is low enough that they fly over it. Also, the ceiling is high enough that they can easily land.
Normally, flights are only cancelled if visibility is zero or there is a storm right over the airport. On a prog, you look for stuff like this:

If this is right over the airport, then that is bad. If there is a storm on the flight path, then they just go around it.

Flights might also be canceled for many other weather phenomenon including heavy snow or ice, visibility below the allowable limits (not just zero), winds above allowable limits including sustained, gusts, and crosswind factors, temperatures above or below limits, etc.


text:
How are extreme winds aloft handled and how do they affect flight?
I'm looking at forecasted winds aloft on SkyVector for early next week. Specifically, I'm looking at the Pacific Ocean (routed between California and Hawaii) and notice that there are some barbs showing almost 150kt winds at FL300.
Being someone who only has experience flying in lower altitudes with wind speeds I can fathom, this brings up a few questions for me:

Is there a maximum or safe winds aloft value / crosswind for say, a 737 to fly?
How is it reasonable to deal with wind speeds this high when they're other than a direct headwind or tailwind? What if it is a direct crosswind, how is it possible for the airplane to fly without significant navigation issues (or maybe safety issues?) at velocities that high.
In general, how does the significant wind speeds found in the upper altitudes affect flight (contrasted with typical general aviation flight)

Wind speed is bigger but air is less dense up there. One thing compensate the other in terms of structural load.

Check out this wind  Amazing groundspeed!

Related: Is a wind speed of 150 km/h dangerous during a flight in an Airbus A321?

I like to show people videos of planes flying backwards.
These videos show that wind does not have an effect on how well the aircraft stays in the air - no matter how strong it is, it only effects the path taken over the ground. A steady wind makes zero difference to the aerodynamics, whether it is a piper cub or a 747. The aircraft doesn't know what the wind is doing - comparable to you closing your eyes while floating on a smooth flowing river, you wouldn't think you are moving. The stated crosswind limit is only for landing, when you need to be able to fly in a straight line with precision.
I think the big thing you're forgetting is that the wind correction angle is affected by the true airspeed (TAS). The faster the TAS, the less correction is needed for the same wind. Think about it, if you are travelling forward at a faster velocity, it will take a bigger force to knock you off course. 737s have a TAS of about 400-450kts, so whilst a 150kt wind is strong, it's not all that different to a 30kt wind in a GA aircraft. 99% of the time there will be a crosswind component of some kind, but the method of correction for jets is no different to GA - just point the noise into wind as per your calculations.
Back to flying backwards for a minute. The only safety issue would be if the wind were to suddenly stop. The aircraft indicated airspeed would suddenly be 0 and a potentially unrecoverable stall could develop. But one thing many 'ground dwellers' don't appreciate is that the wind - in fair weather - is actually fairly constant when it is not effected by ground obstacles and friction. Generally speaking, the higher you go, the more steady and predictable the wind will be.

Any aircraft is in a safety issue when the wind suddenly shifts or goes to zero.  Typically, though, this is called turbulence, windshear or even a microburst.  Using your analogy imagine floating down water rapids in a canoe vs. a calm river.

Hi @Ben, I think you addressed my question better than I was able to frame it in the first place. Part of my thought was with winds at such a high velocity, I would think the changes in the wind speed or direction would be much more abrupt and significant. Thus creating more wind shear, etc.

Is there a maximum or safe winds aloft value / crosswind for say, a
  737 to fly?

Crosswind limits are in place for landing not flying. Cross wind limits have to do with how effective the control surfaces are which allows you to fly the plane in such a manner where the fuselage is aligned with the ground track. At altitude winds simply either add to your ground speed or count against it.

How is it reasonable to deal with wind speeds this high when they're
  other than a direct headwind or tailwind? What if it is a direct
  crosswind, how is it possible for the airplane to fly without
  significant navigation issues (or maybe safety issues?) at velocities
  that high.

Winds are not always a direct head or tail wind (for that matter they often are not) thus you simply need to figure out your course correction. You can check out this video on how to do so. Keep in mind that you are flying through the air and thus moving with it, on the ground you feel wind because you are stationary and it is moving around you.

In general, how does the significant wind speeds found in the upper
  altitudes affect flight (contrasted with typical general aviation
  flight)

Its all relative but in general it simply effects time in transit (ground speed). However keep in mind that the planes that fly up there are often faster so 150Kt headwind on a plane that can cruise at 550Kts at FL300 is not all that different from a 35 Knot headwind on a plane cruising at 140kts at 5000ft.

Also, if you have a predicted 150 kt westerly wind at FL300, you would try to fly at that level if westbound, higher or lower if eastbound.

In any plane with sufficiently precise position information available (all of those capable of cruising FL300 have that) you can get ground track indication and just steer to keep that aligned whatever the heading ends up. Or rather the autopilot steers that way; FL300 is in RVSM airspace where you must use A/P (unless you have special clearance with non-reduced minima, which you usually won't get).


text:
Are there any aircraft geometries which tend to prevent excessive bank angles?
For thousands of years humans have worked out that putting sufficient weight sufficiently far down in the hold of a ship makes it less likely to capsize. Obviously a ship tends to bounce back to an upright position if it has a good ballast arrangement, and it's only if you go beyond a critical tipping angle that the gravity situation works in the opposite way and you capsize catastrophically.
Are there or could there be any aircraft geometries which would do that somehow with respect to roll? I.e. tend to tip the plane back to level flight, with a higher force the greater the roll (until you get to a critical bank angle, when it doesn't work any more)? I realise that an aircraft's situation is nothing like a ship's, not least because a ship straddles two media.
I'm wondering about geometries where the wings are above the fuselage, for example... and maybe above the engines...? And/or possibly flexible geometries which somehow transform without being commanded, simply due to the effect of aerodynamic forces on them, but do so in such a way that they intrinsically promote stability.
I also realise the answer to this may be "no, absolutely impossible". But if so, how could that impossibility be proven?
Later edit
These are very interesting answers and give me much to think about.
I just thought of something rather extreme conceptually but quite ship-like: supposing after a plane took off, the luggage hold and maybe a fuel tank swung down on a pole a few metres long attached to the underneath of the fuselage, which then locked into position making it rigid? Wouldn't such a plane find banking very difficult, and wouldn't it be that the more you wanted to bank the harder it would be? In other words if the centre of gravity is located under the plane can't you achieve something like this?
NB I'm not advocating this as a desirable design, and shudder to think of the multiple technical reasons why this would be BAD, just wondering whether it would make rolling away from level flight difficult, and make righting occur without any intervention by human or computer, and making control surfaces less effective the greater the bank.

I recommend you search using the term "stability", "dihedral" etc. - both here, and in other places.  There is lots of information out there on roll stability...

Are you aware that, in stark contrast to a ship, rolling is a way of steering th airplane. This is essential, not a movement you want to restrict. Rolling an airplane is absolutely necessary. Besides, just FYI: restrictions today can be implemented using software to keep the airplane in a safe angle, and whether this should be there or not is a large philosophical debate (Boing vs Airbus, the former "doesn't", the latter does). But it all boils down to the fact that rolling is desired in an airplane. It's never desired on a ship.

@Mayou36 yes, and in anticipation of your sort of observation that's why I said, clearly enough I had hoped, that the situations were radically different. The idea of the question is not whether a self-correcting roll control system design/mechanism is desirable in an aircraft but whether it's possible.

@Mayou36 if your water craft is small enough, roll (known as "edging" a kayak) is used in steering. By lifting one side of a kayak with your knee you can turn quite nicely, It's easiest to demonstrate  by paddling in a straight line then stopping paddling, but can be used with a nice symmetrical forward stroke as well.  Of course there are also turning (yawing) paddle strokes executed in various ways and positions; these are often used in combination with edging

@mikerodent your edit "rather extreme conceptually but quite ship-like" didn't seem to suggest that. The point is, the answer is a clear "yes, you can, the simple Dihedral angle" but there is no_point_ to do more extrem. Sure you can. I think your edit is more a question of a specific design that you have in mind (which won't work!), but that sounds like a different question (One thing is to ask if there are designs, another thing is to ask if something work). If you keep then editing the question, the answers will change.

Tongue-in-cheek: If you have a rotationally symmetrical (i.e., circular) wing banking isn't even a known concept!

All those pendulum believers should wonder how a stone and sling works - lateral acceleration - that's what the wing does in a turn.

Dihedral angle
Virtually all airplanes have a certain amount of dihedral angle to the wings -- which is to say, the wings are angled slightly up when you look at the aircraft nose-on. This slightly decreases lift, as the direction of lift is no longer straight up, so there's a slight efficiency loss, but the benefit is that it makes the airplane inherently roll-stable.
The aerodynamics of how this work have been discussed in a previous post on this stack.

High wings
High wings do help with roll stability as well, but it's not as simple as it is in water, so I'm just going to link to a different discussion from this stack about how a low CG contributes to roll stability, and the previously linked post goes into this some as well.
But not to extremes
Now, that said, those are both relatively minor forces. They make a plane more stable in level flight, and if you put in a bank and then release the controls, they'll act to bring you slowly back to level, but they don't really act to stop the pilot from causing an extreme bank. Obviously we don't want innate roll stability to stop us from intentionally rolling the plane, and extreme roll is almost always the result of a pilot's inputs (unless it's physical damage to the wing, but that almost never happens).
A ship has no direct control over its roll and thus needs a strong self-righting impulse, while in an aircraft, roll is one of the main control inputs. We can trust the pilot to do most of the work of bringing the plane back to level after a maneuver, and the small self-righting effects are just making it easier to keep the wings level.

The pendulum effect does not occur in airplanes. Maybe I’m misunderstanding and you mean something else by pendulum effect?

Y'know, there's a lot of misuse of terms related to that, so I'll delete that part and just reference a different q on here that addresses it much better.

"A ship has no direct control over its roll" There are ships that have active stabilizer flaps that can control roll.

In your explanation of dihedral giving stability, it's not obvious why only vertical lift would matter.  If the plane is banked, it's no longer just the horizontal plane that matters for roll-inducing torque calculations.  It's lift perpendicular to the line connecting the wingtips, or something like that.  e.g. in an 80 degree bank, most of the lift is horizontal, but ailerons still work the same way by making one wing lift more than the other get the plane to roll out of the bank.  I don't dispute that a dihedral gives roll stability, but this explanation doesn't seem right.

Well, I think it has to do with the horizontal force inducing a small sideslip but I'm not actually sure that's right.

Koyovis's answer on Contribution of wing vertical location to roll stability (linked from their answer on this question) makes sense to me: it is indeed about sideslip creating extra pressure under the low wing because it angles upward relative to that component of airspeed.  That answer also says some about high vs. low wings.

The shapes themselves do not affect roll stability, it is the effect of motion (and aerodynamic resistance, aka drag) that creates or inhibits rolling motion.
Going back to the ship.  If one had sufficient force (wind, sails) to push it sideways with all the weight at its lowest point, it would roll (heel) sideways away from the wind.

does the weight right the ship like a "pendulum"?

When one considers torque around the Center of Mass, one can see that the bouyant force on the heeled over side counteracts the rolling force of the wind.  Putting the weight lower in the ship increases the righting torque of bouyancy.

how else to increase the righting torque?

A wider beam.  This is what humans may have done thousands of years earlier ... the catamaran.
How else?  A lower sailtop, such as this.  Lower draft enabled these ships to navigate much shallower waters ...
Back to aircraft.  Dihedral creates a righting roll torque imbalance, but is counteracted by the turning tendency a roll creates.  The correction for this is to have more side area above the center gravity$^2$ (such as a tall tail) to roll the plane away from the nascent turning motion.  This is part of the reason "highwings" are considered more stable.
Lastly, we consider aerodynamic forces from the sideslip of an "uncoordinated" roll$^1$.  Higher pressure under a highwing/fuselage area tends to roll back the aircraft upright, whereas lower pressure over a low wing/fuselage will not.
$^1$ where yaw is insufficient compared with bank angle
$^2$ or to lower the center of gravity!

Are there any aircraft geometries which tend to prevent excessive bank angles? Well, no, I'm not aware of any aeroplanes that cannot do a full 360° roll. Ailerons are deflected, and the result is an aerodynamic rolling moment dampened by the back pressure of the air. Sustain an aileron deflection high enough, and the aeroplane rolls through all 360° of bank angles.
What is desirable in this procedure is that there is a linear function between pilot wheel deflection and aeroplane sustained bank angle, which is provided by the side slip occurring in a turn, as depicted in this answer. And yes, high wing configurations have a built-in roll reduction factor, which sometimes needs to be reduced by anhedral (wings pointing downwards).

Thanks. This makes me wonder why you'd ever need/want to reduce the roll reduction factor on a plane: can't you always steer using the rudder? But that's another question! ... which I'm going to try to look up.

Could check this one, mentioning the Fokker Spin which only turned using its rudder. It's slow though, and introduces sideways accelerations.

Despite somewhat confusing terminology in the title, the OP is not asking about a control surface / AOB roll limiter, they are asking about positive roll stability. The body of the question provides needed context.

When searching for features which make airplanes inherently stable, I propose to look at free-flight model airplanes. What is it they do differently?
Long tail lever arm
The most striking difference to manned airplanes is a small tail on a very long rear fuselage. Since aerodynamic damping grows with the square of the distance between wing and tail, this gives model airplanes very high damping (not stability - this is in the ordinary range). As a consequence, all rotations happen very slowly. This includes roll, here because free-flight models also use high-aspect ratio wings. This also conveys high roll damping, so all three axes are highly damped.
Other features are more conventional.
Dihedral
What is striking is low dihedral of the center wing coupled with high-dihedral wing tips. The overall dihedral is, however, not so much different from regular airplanes because you want roll resulting from sideslip to be in a specific range. Too much and you will end up with an unstable dutch roll!
The high or low wing mounting will only affect how much dihedral is needed to achieve the right amount of sideslip-induced roll, so it does not affect  stability directly. Please forget all the nonsense on the web about "keel effects" and "pendulum effects", which are a fallacy. Dihedral all by itself cannot prevent the buildup of roll angles. All it does is to add a correcting roll moment in sideslip conditions.

No. Aircraft geometry interacts with applied forces and gravity to produce a state space - position, velocity, acceleration, and attitude. The problem is the geometry can't tell the difference between applied forces and gravity, so it doesn't have any way of getting an Earth Horizon reference for roll angle.

I thought someone might say something along these lines. Essentially that aerodynamic forces are typically so great compared to the force of gravity that nothing like this can work. And another way in which situations of ships and aircraft are completely different. However, this seems to overlook the fact that gravity is non-zero, and ALWAYS points in one direction, i.e. perfectly perpendicular to the horizon. See my "extreme scenario" (in the question).


text:
Is there a list of CASA prohibited medications which would disqualify a pilot from flying or obtaining a Class 1 medical?
Is there a list of medications which would disqualify a pilot from flying or obtaining a Class 1 medical?
Prior to having my medical I want to know if any medication I am likely to take will disqualify me, so that I can make enquiries about switching to an approved alternative.
A link to a list of prohibited or otherwise troublesome medications or similar online resource would be ideal.

There is no all-encompassing list of 'banned' medications publically available for Australia. In the regulations there is a 'catch all' to the effect of "pilots must not take any medications which may inhibit their ability to fly safely".
If you want specific advice on a specific medication, why not give CASA a call? That or you can see a DAME (which is a GP qualified to do aviation medical assessments).
What you can find out there is general advice though. Although questions such as this on ADHD and this more generally refer to the US system, the Australian restrictions are not too dissimilar.
Broardly speaking, Ritalin and other 'depressants' are incompatible with flying. Bi-polar disorder faces many restrictions but stable depression is manageable. I did hear somewhere that you need to be off antidepressants for 12 months though. Diabetes and blood thinning medications are OK but subject to regular testing and scrutiny.
As an aside, sometimes CASA, instead of outright refusing the medical, will place restrictions on it instead. This can be things like you must fly by day VFR only, or you can only fly with a qualified pilot next to you.
EDIT: I found this page from the CASA website which has a list of medications to stay away from. It's not exhaustive but it's a start


text:
What could cause an inadvertent squawking of 7700?
I get alerts whenever a plane squawks 7700, using a popular flight tracker application. It happens quite frequently that the aircraft, reported to squawk 7700, in actuality squawks 7550 or some other benign number.
What would cause this? Are the instruments such that it starts on 0000, and allows setting each digit with a dial you can turn both left and right?

I'd add that most tracking websites, if they're reporting 7700 or similar, it can often be a decoding error of the data that it's getting and get corrupted.

Could be—I've seen squawks like 0353 after alerts.

"a popular flight tracker application" is not a certified source

@SteveKuo true, but the point of the question was more the mechanics of the transponder. You could probably remove the reference to the flight tracker entirely if you want.

A transponder in most planes look something like this

(source)
The code is changed by turning the knobs beneath the numbers. Lets say you are assigned 5700 as your code but your previous code was 7456. If you are careless or start from the right most knob your transponder will briefly be set in 7700 until the most significant digit is changed. If the radar does a pass (interrogation) at that time ATC will momentarily receive a 7700. Some people say you should put your transponder in standby (SBY) mode when changing codes to avoid this happening.
Some GA planes (and even some larger planes) have newer digital interface transponders like this one,

(source)
These make it a bit harder to pass through the codes since you are not turning knobs but in bumpy air you could accidentally double tap a number. For example lets say you are assigned 7003 in bumpy air. You go to hit the 7 and accidentally double tap the button. Then you type in the 00 and your code is complete by the time you hit the 3.
After some looking it seems that larger aircraft user a transponder like this one,

(source)
In this case you will see a similar case to the first transponder listed. If its not in STBY while switching you inevitable have to pass over 7700, 7600 or 7500 to get to some codes. If an interrogation happens at that time it may cause the results you mention.
In terms of switching to STBY mode, the only documentation I can find about keeping the transponder in altitude reporting mode is this document which states

operators and pilots of the need to ensure that transponders are in the
  altitude reporting mode whenever their aircraft is on an airport movement area at all airports.

This was issued in May of 2015 and seems to be related to the ground surveillance systems being installed at airports.
The FAA FAR touches on transponder operation in S91.215 and part C reads

(c) Transponder-on operation. While in the airspace as specified in paragraph (b) of this section or in all controlled airspace, each person operating an aircraft equipped with an operable ATC transponder maintained in accordance with Sec. 91.413 of this part shall operate the transponder, including Mode C equipment if installed, and shall reply on the appropriate code or as assigned by ATC.

This section simply states that you must "operate" the transponder on the code assigned while in required airspace. That seems a little vague and does not completely exclude putting it in STBY mode to switch codes.

For example lets say you are assigned 7003 in bumpy air. You go to hit the 7 and accidentally double tap the button. Then you type in the 00 and your code is complete by the time you hit the 3. <-- This is what that nice friendly "CLR" (CLeaR) button is for.  Most pushbutton transponders have one :)

I was more presenting the situation where you did not realize you had double tapped the button and were somewhat careless in your typing but you are correct ;)

Some people say you should put your transponder in standby (SBY) mode when changing codes to avoid this happening. - Note that ATC discourages this, and expects the transponder to stay on ALT and the pilot to change codes with care to avoid emergency squawks.

I was taught to always use Standby when changing squawks for exactly this reason. I assumed this was universal but it seems to be encouraged at least in the UK.

See my edits (they apply to the FAA regs)

Just change the code, don't put in standby, straight from ATC https://www.youtube.com/watch?v=41UScn6SLcU

In the older GA transponders where the code selection was made by turning knobs, the electrical contacts are made thru wafer discs in the back of each individual knob, with time and constant use is possible that the digit indicating disc slips and you'll end up squawking a different code than the displayed on the unit.

We had an incident in Denmark years back where the disc for the second digit had been put in wrongly during maintenance, so that it was indicating one digit to the right of what it was actually transmitting. The pilot happily set his transponder to 7000 (standard VFR code in Europe), which caused quite some disturbance at local ATC units as he was actually transmitting 7700 for the entire flight.

Probably the most common scenario would be switching from VFR to a code in the 75xx, 76xx or 77xx ranges when using a transponder with a control to set each individual digit (or each digit in order):

(source: aircraft-spruce.com)
If you're squawking VFR (as most will be) on approach to a towered airfield and are assigned a squawk code 7625, if you're not paying attention you'll set the 7, then the 6, and at that point you'll be set to squawk 7600 (comms failure). Some IFF systems can interrogate an aircraft several times a second, so if you're set to 7600 even for a second it can cause an alert on the ATC system.
To guard against this, The easiest way is to set the transponder to "SBY" to prevent it responding. As other answers/comments have said, this is questionable because it stops altitude reporting, which can be useful even if your squawk code is wrong while you're changing it. Another possibility with the older four-knob analog-display systems is to set your transponder's last digit first when changing from any XX00 code, and in normal left-to-right order when moving into an XX00 code. Say you're squawking VFR and ATC asks you to squawk 7625. Set the 5 first in the last digit, then the 2, then the 6 and finally the 7. You'll transition from 1200 to 1205 to 1225 to 1625 and finally 7625, all completely innocuous codes (though one might be a dupe of another assigned code; really no way to prevent this except to go to standby or just set the code quickly).
It's also possible for newer digital systems to temporarily enter a standby-like mode while you're changing the code, making it harder to accidentally respond with the wrong code, including an emergency code, while you're still switching it. If you exit the code entry mode halfway through, it can still be an issue, and some of the digital systems mimic the four-knob style and so they don't really know when you're done.


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Based on this fuel flow chart, why isn't it more optimum to remain at an intermediate altitude rather than climbing?
I am having a bit of confusing as to why people say planes gets more efficient as they fly higher. Because on a typical long haul flight the Fuel Flow of the aircraft will obviously be much more that when it was lighter as it was heavy but my main question is since aircraft FF decrease with weight but at the same altitude isn't it more efficient to keep flying at the same altitude instead of climbing further? Here below are some charts on the B737 FF getting lesser with the altitude as it gets lighter. Notice how the FF goes up as you climb higher even though its lighter. Looking at the charts I suppose isn't it more efficient to keep flying at the same altitudes? Can anyone help me clarify this? Thanks

If you stay in the gray boxes, every time the aircraft gets lighter your fuel flow decreases, even though you may have to fly higher to stay inside the gray. For example, from 60000 kg at 37000 feet, if you reduce the weight to 50000 you have to climb to 38000, but the fuel flow decreases from 1135 to 1055. At a given weight, of course, there is an upper limit to how high you can fly, and being too close to that limit isn't good. So obviously "fly higher to save fuel" is a gross oversimplification.

When airplane mass, altitude, N1 (engine spool speed) and Mach number change together, it is very hard to come to a meaningful conclusion what is better for fuel flow. However, you see that the grey boxes tend to show the smallest fuel flow and they sit at the upper altitudes, so altitude seems to help. Going above 90% N1, however, seems to increase fuel flow again.
With increasing altitude, the flight Mach number needs to be increased to keep indicated airspeed constant. I expect that the chart lists trim points at or near the optimum polar point for cruise, at least that is what the almost constant indicated airspeed for each mass suggests. With increasing Mach, drag goes up but so does the distance covered per time, so there is again an optimum where the transsonic drag increase is still tolerable and outweighed by the higher speed over ground.
Therefore, higher flight speed is one reason why airliners like to climb to the tropopause. But there is more:
The thermodynamic efficiency of a heat machine grows with the ratio of temperatures in its thermodynamic cycle. Since the lowest temperature is determined by outside air, and outside air temperature drops with altitude while the top temperature is limited by the engine's materials, flying higher improves the thermodynamic efficiency of the engines.

So if in general optimum doesn't necessarily mean better fuel flow only? It involves many factors like these? Looking from the charts, I am assuming now I am taking off with the weight of 70 tons and I will cruise at FL330 and after say I burned of some fuel and I am at 65 tons now and I want to step climb to FL350, the improvement of fuel flow from 330 to 350 looks very small. And the n1 has increased to 87 from 85. Is this how a step climb is done?

@JoeWie: The optimum is defined in a very practical way: To quickly get a defined payload from A to B for the least amount of fuel. Quickly, because faster aircraft can fly more trips per day. This can be expanded: To fly a defined payload from A to B with the smallest possible fleet and the least amount of fuel. For step climbs please look here

Doesn't also propulsive efficiency of turbines increase with velocity due to the pressure recovery? That is another reason to fly high where the true airspeed is higher.

@JanHudec: No, efficiency gains are from lower ambient temperature. Pressure recovery increases mass flow and thrust, but the fuel flow has to match the air mass flow and efficiency is not improved.

@PeterKämpf, Hm, I mixed in the pressure recovery incorrectly. Actually I meant due to the lower difference between intake and exhaust velocity, since the exhaust velocity remains fairly constant.

@JanHudec But speed lowers the efficiency numbers, at least when expressed as SFC. See here for example. Work has to be done to slow down the intake flow (actually, to speed it up, but you know what I mean) and then again to push it out at the back.

@PeterKämpf, yes, speed lowers the SFC, i.e. increases the efficiency (efficiency is power to fuel flow, SFC is fuel flow to power). That's what I am saying.

@JanHudec: No, speed increases SFC.

@PeterKämpf, if for turbojet TSFC does not change much with speed, then SFC has to decrease with speed, because SFC = TSFC / speed. In the linked answer, $\eta_{total}$ has $v_∞$ in the numerator, so it (efficiency, so reciprocal of SFC) increases with speed (keeping TSFC, $\frac{Q}{T}$ constant).

@JanHudec Sorry, SFC in a jet for me is always thrust specific. So I meant TSFC all along.

@PeterKämpf, yeah, TSFC does grow with speed (only a bit for turbojets, more for turbofans), but SFC decreases. And since getting from point A to point B at similar drag (only a little higher at higher altitude) requires similar amount of work, the decrease in SFC is what matters.


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What is the drag (or $C_D$ vs $C_L$) of the Airbus A320 in cruise flight?
Is there any website or data-sheet that I can find drag of airplane for cruise conditions. $C_D$ vs $C_L$ graph is also acceptable.
To be more specific I am searching drag values of A320 in cruise flight.

In unaccelerated, straight and level flight, total drag is equal to total thrust. Perhaps you may find the data on the total thrust provided by the engines of the A320 under cruise conditions. That would answer your question.

Thank you for your answer, I cannot find a website that provide information about cruise thrust

Try to find the best L/D for the A320. Probably, that's also the L/D at cruise flight. From the weight of the A320 and the L/D, you can easily compute the total drag of that airplane...

At level flight, constant speed, the total drag is not equal to total thrust , since total thrust is weight related. So certainly not in «  accelerated » flight

I need to make a few assumptions to close the gaps in the data you provide.

The aircraft flies close to its optimum L/D - which is 18 for the A320-200 in cruise. So the $c_D$/$c_L$ is 0.055556.
The aircraft is close to its maximum take-off mass, minus fuel for climb. Let's pick 76 tons.

Now the drag force is 1/18 of the weight force. Weight is mass times gravitational acceleration: 745,300 N. So drag would be 41,406 N at this point.
At the end of the trip the aircraft has burnt through 15 tons of fuel; now the drag is a mere 34,300 N. Note also that it now is flying quite a bit higher than initially in the flight, so both friction and induced drag have become smaller.


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If I need to do a course reversal before initiating an approach, do I need to notify ATC that I'm doing it?
If I need to do a course reversal before initiating an approach, do I need to notify ATC that I'm going to do the course reversal, or is it implied that I'm going to do it?
For example:

If I'm approaching the VIR VOR with a course of 230, I would need to do a course reversal to get established on the outbound course. Should I notify ATC that I'm going to do the course reversal?

Why would you do a course reversal? Wouldn't you just turn prior to the IAF to intercept the outbound course?

Which country or regulator are you asking about? Bolivia?

@JonathanWalters Because ICAO states the following about base turns: "Unless the procedure specifies particular entry restrictions, reversal procedures shall be entered from a
track within ±30° of the outbound track of the reversal procedure. However, for base turns, where the ±30° direct entry
sector does not include the reciprocal of the inbound track, the entry sector is expanded to include it." So with a course of 230 I would be outside of the "entry sector" for the base turn.

@Pondlife Yes, Bolivia.

If in doubt, it's better to advice ATC one time too many.

@Luis Eduardo Vaca, I would expect a racetrack followed by a base turn, with the racetrack getting you into an entry sector.  The implication is that you have to do the course reversal, and therefore do not report it, but the requirement is that you do a racetrack to setup for the entry sector. Does that address your concern?

@J.Hougaard: agree completely. When uncertain, tell ATC. Only once have I had ATC complain, slightly, when I told them I was executing a (charted) course reversal maneuver. Otherwise, ATC has simply acknowledged my transmission. (This is in the U.S.)

@mongo Yes it does, however like J.Hougaar said it's better to just tell them that I'm doing it, specially since we have no radar service here.

Suggesting "tell ATC anyway" doesn't answer the question.  He's. It asking for advice but for facts.

It is implied.
When you are cleared for the approach you are cleared for the procedure turn, or base turn as indicated on the plate.  Since your current heading puts you outside the entry sector, you do a racetrack to get aligned with the entry to the base turn.
It is always good to know when you have to call and when you don't because there could be heavy traffic, high workload, or who knows what. But if we're talking a competency ride or something like that, you should know whether you need to make the call or not.  All that said, one can of course report the course reversal if there is doubt.
In this instance, there is no requirement to report the turn.


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Are the "centerbody", "fan hub frame", and "intermediate case" all the same thing or separate parts?
I'm curious about the frames & cases at the front of an engine. I've seen OEMs call them the centerbody, fan hub frame, and intermediate case. Are these all the same thing or are these each a separate part? It seems that each OEM has their own vocab.
The fan case is the one I can figure out. I'm more talking about the area right behind it before the HPC

You mean "cowls" don't you?  Case refers to the engine itself.

I'm referring to the engine, not the nacelle. Everyone seems to use the same vocab to describe that so it's pretty clear.

Welcome to aviation.SE! This seems like a case where a picture would be very helpful to clarify what you're asking. Can you upload or link to one that shows the components you're asking about? You might also like to check out the [tour] to see how this site works.

If your question is "are centerbody, fan hub frame and intermediate cases the same thing?" you may edit the title to reflect it. It make it easier to crawl in a list of questions about the same topic. Moreover, you should transform the title in a question as this is a Q&A website.

On Boeing aircraft, the "centerbody" is part of the exhaust system.  It is the inner is the inner part of the exhaust as shown in the picture below (the outer part being called the primary nozzle).  The centerbody is also referred to informally as the "plug".  Since your question seems to be asking about fan and compressor cases, this doesn't seem to fit.  I'm not sure what Airbus or other airframers call this part, so maybe the word "centerbody" is used differently in different contexts.  But for a Boeing airframe, that's the centerbody.
For turbofans which use a "quick engine change" concept, the fan frame actually splits into two pieces.  The "fan hub frame" referred to the inner part.  Hence the word "hub" in the name. I've marked it up in the image below.  This photo also illustrates the concept pretty well.  This shows an engine being assembled.  The outer part of the fan frame (with fan case attached) is on the right, and the fan hub frame (with the rest of the engine core attached) is on the left.  The "fan hub frame" proper is the part just to the right of the yellow tape.
The term "intermediate case" is ambiguous to me.  I could think of two or three different things that that might refer to. On a two spool engine, that probably refers to the booster case, which is usually immediately forward of the fan frame.  But on a three spool engine, it probably refers to the intermediate compressor case, which is usually just aft of the fan frame. Do you have more context?

Thanks! For the intermediate case, I'm referring to the diagramn on page 3: https://www.gknaerospace.com/globalassets/downloads/sweden/aes_product_key_standing_a4_screen.pdf/.  Hard to tell, but it looks like there is a second major frame or case behind the fan hub frame. Am I crazy or is this a thing?

Can you mark up the drawing and point out the specific area that you have questions about?  Still not sure I understand what you are asking... "behind" to me typically means "aft", but the thing labeled "intermediate compressor case" is forward of the fan hub frame, so not sure that I understand what part you're talking about